The reason they call is because it is their job to get every evaluation completed in a satisfactory fashion with the lowest payout possible. He/She is hoping he can use pressured language like "So can I count on your to do these jobs" to get you to agree to do them for less than a fair price.
If you are indeed the only person in your area working for the company, you are in a position of strength. Simply give him/her the minimum dollar amount you will accept for the shops and then be politely firm. Unless they are able to recruit a new shopper in your area or convince someone to travel in for a low fee, you will get your fee.
I have never had anyone say so I can count on you to do these jobs. I have been asked if I am interested in doing them.
I received a few phone calls asking to take up two jobs outside my comfort zone for the same price stated up on the job board. I waited for the nice man to tell me he was going to raise the price so out of the blue he say's "So can I count on your to do these jobs"? I asked him "How much extra are we talking about"? He said "Oh, I do not have the authorization to raise these jobs because their towards the high end of our range". So I said "well, their outside my normal range of driving and I wish you luck finding another shopper to get them done". He offered me the same pay offered on the Job Board. I apologized and bid him "Good Evening" so he calls back ten minutes latter offering $2.00 more if I promise to take three of the jobs they need help with.
If a scheduler calls and offers a shop at the rate that it's posted at, I usually tell them that I'll review my schedule and assign it on the site if I'm interested in it.
If they're calling and not offering an incentive, then there's no rush or limited time: it's probably still going to be available in a few minutes and I've even probably already seen it on the board or seen an email (or 50) about it. I find that I like to review shops while sitting at my desk with my calendar open so that I can see what else I have scheduled for that time.
If I'm going to accept a phone offer for a shop, there needs to be a bonus or other incentive to make it worth making an on-the-spot decision.
Jot down the number so that you can caller ID next time. I don't pick up for the lowballers. They go to the answering.